1. Field of the Invention
This invention relates to an electronic parts mounting method in which electronic parts in parts feeders are picked up by a plurality of nozzles which are provided to a transfer head, and then are transferred to and mounted on a board.
2. Related Art
There has been extensively used the type of electronic parts mounting apparatus for transferring and mounting electronic parts (hereinafter referred to as "chips") on a board, in which while horizontally moving a transfer head in an X-direction and Y-direction by a moving table, a chip, stored in a parts feeder, is held by suction by a lower end of a nozzle on the transfer head, and is picked up, and is transferred and mounted at a predetermined coordinate position on the board.
There has been proposed another electronic parts mounting apparatus of this type (Japanese Patent Examined Publication No. 3-70920) in which chips, stored respectively in a plurality of parts feeders juxtaposed at a pitch, are simultaneously picked up by suction respectively by a plurality of nozzles mounted in a row at a pitch on a transfer head (This operation will be referred to as "simultaneous picking-up" in the present specification), and are transferred to and mounted on a board. This method has an advantage that the mounting efficiency is greatly enhanced since the plurality of electronic parts are simultaneously picked up at a time by the plurality of nozzles.
However, in the electronic parts mounting apparatus of the type in which the chips in the plurality of parts feeders are simultaneously picked up by the plurality of nozzles, the rate of chip pick-up mistake is higher as compared with the type of electronic parts mounting apparatus for picking up a chip in one parts feeder by one nozzle. The cause for this is mainly due to the following reasons.
In this kind of electronic parts mounting apparatus, the pitch of the plurality of nozzles is set to an integral multiple of the pitch between the parts feeders so that the chips in the plurality of parts feeders can be simultaneously picked up by the plurality of nozzles. However, because of various errors (including an error in the mounting of the nozzles on the transfer head, an error in the assembling of the parts feeders, and an error in the juxtaposition of the parts feeders), the pitch of the nozzles fails to be accurately an integral multiple of the pitch between the parts feeder (more correctly, the pitch of the chip pick-up positions between the parts feeders), and thus a slight pitch error is inevitable. Because of this pitch error, all of the plurality of nozzles could not simultaneously pick up the chips in the parts feeders, so that a pick-up mistake was liable to occur.